BRCA1/2 mutations and FMR1 alleles are randomly distributed: a case control study

BRCA mutation carriers were reported to display a skewed distribution of FMR1 genotypes, predominantly within the low normal range (CGG repeat number <26). This observation led to the interpretation that BRCA1/2 mutations are embryo-lethal, unless rescued by 'low FMR1 alleles'. We undertook to re-explore the distribution of FMR1 alleles subdivided into low, normal and high (<26, 26-34, and >34 CGG repeats, respectively) subgenotypes, on a cohort of 125 Ashkenazi women, carriers of a BRCA1/2 founder mutation. Ashkenazi healthy females (n=368), tested in the frame of the Israeli screening population program, served as controls. BRCA1/2 carriers and controls demonstrated a comparable and non-skewed FMR1 subgenotype distribution. Taken together, using a homogeneous ethnic group of Ashkenazi BRCA1/2 mutation carriers, we could not confirm the reported association between FMR1 low genotypes and BRCA1/2 mutations. The notion that BRCA1/2 mutations are embryo-lethal unless rescued by the low FMR1 subgenotypes is hereby refuted.